Lapping valves

Is the best way still with the suction cup tool, or could i chuck it in a drill? I have 16 to do on the 2.4....

I have done it both ways, but preferred way for me is chuck it in a drill. Well, a bit of hose chucked into drill stuck to end of valve. 

Work part time in machine shop. I do a lot of lapping & vacuum testing. Here's my weapon of choice.

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So can you guys elaborate on how you're doing the drill method? I figure if you guys are doing it and having success you must have a way that works that I can copy

I just wrap a little electrical tape around the stem, attach my cordless drill, smear some grinding paste on the seat, and pull and release about 20 times. It's easy to see when you have a nice pattern after you wipe the paste off. Drill on low speed.

How long do you hold the trigger? And both directions or just one?

The Snap-On suction tools I use come in different size suction cups and have a shaft that fits in 3/8" drill. https://store.snapon.com/Valve-Lapping-Tools-13-16-Power-Valve-Lapping-Tool-P891152.aspx  I like the cordless Milwaukee drill because it's light and has good trigger control to start turning slowly. Apply a little lapping compound to the 45 degree face of the valve (small amount like a couple drops total per valve), drop valve in head (with head up off bench on stands or wood blocks), push suction cup onto head of valve with cup centered on valve. Start drill slowly with very little downward pressure and bring revs up a little, spin maybe 10 seconds. If you try to go too fast the suction cup will pop off, that's your speed limit. Remove valve, clean compound from both surfaces and check pattern on head & valve. If you see both surfaces have been marked all the way around by the compound move on to next valve. If not repeat process.

When done lapping check each valve with vacuum tester. Depending on heads some have exhaust ports for emissions stuff that you'll need to plug to vacuum test exhaust valves. Because there's no spring pulling the valves tight to vacuum test pop each valve in place a couple times & hold tight when applying vacuum.

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